1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light. [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma-rays].
2. Description of the Prior Arts
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photo-conductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics corresponding to those of electromagnetic waves to be irradiated, a good response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si] has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and U.K. Laid-Open Patent Publication No. 2029642 an application of a-Si for use in photoconverting reading device. However, the photoconductive members having photoconductive layers constituted of a-Si of prior art have various electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light as well as environmental characteristics in use such as weathering resistance and humidity resistance, which should further be improved. Thus, in a practical solid state image pick-up device, reading device or an image forming member for electrophotography, they cannot effectively be used also in view of their productivity and possibility of their mass production.
For instance, when applied in an image forming member or a photographic device, residual potential is frequency observed to remain during use thereof. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, according to the experience by the present inventors from a number of experiments, a-Si material constituting the photoconductive layer of an image forming member for electrophotography, while it has a number of advantages, as compared with Se, CdS, ZnO or organic photoconductive materials such as PVCz or TNF of prior art, is also found to have several problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the photoconductive layer of an image forming member for electrophotography having a photoconductive member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional photographic method. This tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained at all before development.
Thus, it is required in designing of a photoconductive material to make efforts to obtain desirable optical and photoconductive characteristics along with the improvement of a-Si materials per se and to make a photoconductive member capable of obtaining stable image-quality with high sensitivity.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices or reading devices. It is now been found that a photoconductive member elaborated to have a layer structure comprising an amorphous layer exhibiting photoconductivity, which is constituted of so called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon which is an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon [hereinafter referred to comprehensively as a-Si(H,X)], and prepared to have a specific composition as described hereinafter, is not only usually useful but also has characteristics superior in substantially all respects to those of the photoconductive members of prior art, especially markedly excellent characteristics as a photoconductive member for electrophotography with respect to photosensitivity and stabilization of image quality. The present invention is based on such finding.